Postgres 7.3b1 + pg73b1jdbc3 rs.last() error

Greetings,

I have a problem running the following code:
...
rs = st.executeQuery("SELECT * FROM foo");
...
rs.last();

I get:
Exception in thread "main" java.lang.NullPointerException
at
org.postgresql.jdbc2.AbstractJdbc2ResultSet.last(AbstractJdbc2ResultSet.java:414)
at tjdbc.main(tjdbc.java:53)

The table foo has one record;

JAVA is:
java version "1.4.0_01"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.0_01-b03)
Java HotSpot(TM) Client VM (build 1.4.0_01-b03, mixed mode)

JDBC driver is: pg73b1jdbc3.jar

Many thanks for your suggestions!

Best regards,
lwd.